The present invention relates to an apparatus and method for transmission/reception carrying out transmit power control, mounted on a communication apparatus in a mobile radio communication system.
CDMA (Code Division Multiple Access), one of radio communication access systems, is an access system in which a same frequency or same time is shared by a plurality of users. In the case where a desired transmitting station is far and an undesired interfering station is near, if these stations carry out transmission with same power, the signal level from the interfering station is greater than the signal level of the desired transmitting station, causing a problem of rendering communication impossible.
In a terrestrial mobile communication system, one of the causes of deterioration of channel quality is fading. Along a terrestrial mobile communication propagation path, a signal sent from a base station is reflected, scattered or diffracted by buildings near a communication terminal, producing a standing wave. When the communication terminal moves amidst this standing wave, the level of the signal from the base station reduces in proportion to the traveling speed causing fading by which the reception quality deteriorates.
Therefore, a cellular system using CDMA solves the above problem through transmit power control (TPC), which compensates fading fluctuations and keeps the reception level constant.
Typical examples of transmit power control are closed-loop transmit power control and open-loop transmit power control.
Closed-loop transmit power control is implemented by the other end of communication measuring an SIR equivalent to the reception quality for the transmission signal from the transmitting station, sending a control command (hereinafter referred to as xe2x80x9cTPC commandxe2x80x9d) which reduces transmit power when a measured SIR value is higher than a target SIR and increases transmit power when the measured SIR value is lower than the target SIR through the reverse channel, and therefore closed-loop transmit power control is a method of controlling transmit power based on the content of the TPC command.
On the other hand, open-loop transmit power control is a method of controlling transmit power by subtracting the reception level from a known transmission level of the other end of communication, calculating the level of loss along the radio path and adding a target reception level of the other end of communication to this level of loss.
However, closed-loop transmit power control involves a large control delay and has difficulty in controlling dynamically, having a disadvantage that the communication quality of the system may drastically reduce when high-speed fading or intense interference emerges.
On the other hand, open-loop transmit power control cannot handle the case where an appropriate reception level varies from one base station to another, which may cause offset errors at the reception levels of the base stations, and moreover open-loop transmit power control cannot compensate reception level measurement errors for every communication terminal, resulting in the necessity for increasing the measurement accuracy on the receiving side of the communication terminal.
That is, both closed-loop transmit power control and open-loop transmit power control have advantages and disadvantages regarding transmit power control.
It is a first object of the present invention to provide an apparatus and method for transmission/reception by adaptively switching between closed-loop transmit power control and open-loop transmit power control thereby making the most of both characteristics and compensating reception level measurement errors without the necessity of maintaining high reception measurement accuracy, and providing transmit power control capable of handling cases where high-speed fading or intense interference emerges.
This object is attained by carrying out closed-loop transmit power control using a transmit power value based on a TPC command after establishment of a communication channel, calculating a compensation value based on a difference between a reception-level-based transmit power value and a TPC-command-based transmit power value and carrying out open-loop transmit power control using a value obtained by adding the compensation value to the reception-level-based transmit power value after the calculation of the compensation value.